Hello and welcome! I've used three different combinations. From least to most effective:

1) Hero - Mage; Deathknight - Warrior. This was my default choice, as I always choose a mage as my character and a melee companion seemed the perfect complement. This is an easy configuration to manage: you lead with your mage and can set the warrior to 'aggressive' meaning he'll automatically attack nearby enemies. This frees you up to switch spells and maneuver your mage out of harm's way (since he's leading, enemies will be drawn to him first). The mage gets some powerful spells eventually (like the shaman's hammer and thunderstorm); when an enemy comes on screen, you cast the spell as the DK runs in with weapon in hand to finish the job. Beautiful.

2) Hero - Warrior; Deathknight - Mage. Basically the reverse of the first configuration. I chose this one because of the way the DK's armor upgrades. In option 1, you have to pass up a lot of the cool armor because your strength won't be high enough as a mage, and the DK can't wear much in the way of armor. With this option, though, your hero gets all the high powered gear while you don't have to worry about equipping your (weaker) DK, as his armor will take care of itself. This is a tougher duo. The downside is, the secondary char won't cast spells if he is put in 'aggressive' mode - he'll just run in and bash away with his wand. Meaning, you have to 'lead' with your DK since he's the spellcaster and not the hero. Probably not a big deal for some, and of course you may prefer to manage each character equally rather than have one lead and the other on auto-pilot.

3) Hero - Warrior; Deathknight - Survivor (Archer). By far the most powerful duo. I lead with the hero, who handles a sword or axe (I always go for slashing style), and the DK automatically fires his bow from behind. This team is very tough, many times the DK kills enemies before my hero has a chance to land a hit. But thank goodness you can increase/decrease the difficulty to compensate during a game!

As far as stat points at the character creation screen: the easiest thing to do is choose the "be like" options and pick a class. As far as stats in-game, generally just go with the proportions that are already in place with whatever build you pick. You can also get the Beyond Divinity Guide at the Locus Inn to see what stats and skills you may want to invest in.